gc quiesce

As a part of testing we tried to setup an Oracle 10g(v10.2.0.3) 2-
instance RAC environment hosted on Microsoft Windows 2003 Server ( x64
editioin, SP2 ).
Both machines have 4CPUs (Xeon's @ 2.66GHz) and 4GB of RAM. The are
hosted in VMWare environment.
Storage is implemented using shared hard drives managed by ASM.

What are we trying to achieve is to run an ETL load composed of PL/SQL
jobs in a DSS environment in order to see how the
resource consumption will be balanced through the instances. PL/SQL
code runs without a glitch on non-RAC environment.

Now the problem.
PL/SQL code blocks it's execution usually in a random INSERT statement
( block in other statements were not observed ) by generating a lot
of
'gc quiesce' wait events. However, no blocking sessions were
discovered in gv$session.

PL/SQL code consists of more jobs executed in sequence. Each job has
structure according to this template :

INSERT ALL
WHEN fatal_error_occurs THEN INTO temp_log_table1 (columns) VALUES
(values)

WHEN nonfatal_error_occurs THEN INTO temp_log_table2 (columns) VALUES
(values)

WHEN NOT fatal_error_occurs THEN INTO transient_table (columns) VALUES
(values)

SELECT
columns
FROM
source_tables;

COMMIT;
IF
(ROWCOUNT_IN_transient_table_CHANGED_DRASTICALLY_AGAINST_ROWCOUNT_BEFORE_TRUNCATE)THEN
RECOMPUTE_STATS_ON_TRANSIENT_TABLE;
END IF;
MERGE INTO target_table trg USING
(

SELECT
columns
FROM
transient_table
) src ON (merge_clause)
WHEN NOT MATCHED THEN INSERT INTO (trg.columns) VALUES (src.values)
WHEN MATCHED THEN UPDATE SET trg.columns = src.values

COMMIT;
INSERT INTO log_table1
SELECT * FROM tmp_log_table1

INSERT INTO log_table2
SELECT * FROM tmp_log_table2

COMMIT;
Sometimes the execution blocks when INSERTing data to dictionary
during stats recomputing, sometimes it is the first multi table insert
( in randomly choosed job in the sequence ) that causes the problem.